Wave propagating structure for crossed field devices

ABSTRACT

A wave propagating structure having broad bandwidth capability is disclosed for crossed field electron beam interaction devices. The thermal dissipation characteristics are programmed and customized taking into consideration beam coupling impedance, dielectric loading and suppression of undesired space harmonic modes. A structure such as a modified helix delay line is arranged with groupings of individual elements in parallel and such groupings are serially connected. A fluid coolant is circulated through the delay line and the dielectric constant characteristics of such coolant may be selected to vary the frequency determining dispersion parameters of predetermined portions of the propagating wave.

[451 May 30, 1972 United States Patent Krah et al.

3,241,091 3/1966 Laures................................315/35X 3,237,0462/1966 Olson,.lr.. 315/35 [54] WAVE PROPAGATING STRUCTURE FOR CROSSEDFIELD DEVICES [72] Inventors: Hans-Joachim Krah, Burlington; John S.

q f P m K M 9 l W 6 5 3 8 2 3,250,945 5/1966 Sample Sklenak, Sudbury;William Smith, 3,246,190 4/1966 Boyd et al. Winchester, all of Mass. 3 734 6/1963 ....3l5/3.5 X ...3l5/3.5 X

Sobotka.....

Raytheon Company, Lexington, Mass.

Dec. 28, 1970 [73] Assignee:

Primary Examiner-Herman Karl Saalbach Assistant Examiner-SaxfieldChatmon, Jr. AltomeyHarold A. Murphy Appl. No.:

[57] ABSTRACT A wave propagating structure having broad bandwidthcapability is disclosed for crossed field n e8 6mm Am Pe d c a m a m e mm tnw 1 o.mm w m cllormg yo n w n w 8 h 8 m d m e 0 .m 6.. a e .h g Sdevices. The thermal dissipation characteristics are grarnmed andcustomized taking into consideration b pling impedance, dielectricloading and suppression of unsired space harmonic modes. A structuresuch as a modified helix delay line is arranged with groupings ofindividual elements in parallel and such groupings are seriall fluidcoolant is circulated throu dielectric constant characteristic selectedto vary the frequency determining di ters of predetermined portions ofthe propa u 08 cd XXXX 3 3 1 5O2O 312 355 l3 1 u 2U 3.5mun 3 3i M33 ,3N. 3 93 n 6 .31 u 9 l. u a 3 B 6 m. 5 m3 S mm 1 x u 3 5 m m mm m w m Bm1 m A m m 5 3 .l P n l n" C 3 "u S u u u" 5 E L.m n u n c e n u. M u nA 6 PS6 m a 6 3m e u m" d D CFDSM m mm R E m W.. 86997 N N 66556 u U99999 n u N .l l .l 1 l. L m 9 655 I m d 5 m wmmwn U 1F 1 m m l l l. awAfiwfifi .I. [.l I. 33223 6 Claims, 1 1 Drawing Figures COOLANT INLETPatented May 30,1972 3,666,983

4 Sheets-Sheet 1 COOLANT INLET COOLANT OUTLET RF IN FIG. 2

COLLECTOR waa 22 RF OUT Patented May 30, 1972 4 Sheets-Sheet 9,

Patented May 30,1972 3,666,983

4 Sheets-Sheet 5 Patented May 30, 1972 3,666,983

4 Sheets-Sheet 4 F/G. l0

E OPERATING sToP B A N D BAND FREQUENCY WAVE PROPAGATING STRUCTURE FORCROSSED FIELD DEVICES The invention herein described was made in thecourse of a contract with the Department of the Air Force.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to wave propagating structures for traveling wave electroninteraction devices.

2. Description of the Prior Art Devices of the type under considerationutilize wave propagating structures having a plurality of periodiccircuit elements to retard the velocity of an electromagnetic wave andpermit interaction with resultant net exchange of energy with anelectron beam directed along an adjacent path. The establishment of asynchronous relationship between the electron beam velocity and thephase velocity of the desired space harmonic component of the travelingwaves determines the interaction characteristics. Devices of the M-typeincorporate a sole electrode coextensive with and spaced from the wavepropagating structure to define therebetween the electron interactionregion. Crossed electric and magnetic fields influence the trajectory ofthe electron beam traversing this interaction region. Such crossed fielddevices operate on the principle of transfer of potential energy toresult in amplification or generation of high frequency electricalsignals. Efiiciencies in the order of 70-75 percent and higher areattained together with high average power outputs of many kilowatts andpeak powers of megawatts since an appreciably greater portion of theelectron beam interacts with the waves on the propagating structure.

Another traveling wave device commonly incorporating a wave transmissionstructure of a predetermined periodicity is the O-type. Such devicesoperate on the principle of the transfer of kinetic energy from theelectron beam to the fields of the electromagnetic waves. In suchdevices the combined fields induce the perturbations in the beam to formelectron packets or bunches which exchange energy with theelectromagnetic waves translated along the length of the propagatingstructure when the synchronous relationship is achieved. In such devicesthe coextensive electrode is omitted and the electron beam is directedaxially along the length of the device with the wave retardationstructure circumferentially disposed about the beam. Efficiencies in theO-type interaction device are notably lower since only a small fractionof the electron beam exchanges energy with the electromagnetic waves.Values in the range of to 40 percent are, therefore, common for thesedevices which limits the level of power generated by reason of costlyon-site power requirements and impractically long dimensions. Anexemplary wave propagating structure incorporated in these travelingwave devices is the helix having a plurality of continuously woundcircuit elements in both a unifilar or bifilar arrangement. In the fieldof high frequency electrical signal generation and amplification it iswell known that such helical structures have by far the widest bandwidthcapability extending many hundreds of megahertz and in numerousinstances to octave bandwidths by reason of the high electron beamcoupling impedance characteristics.

The adaptation of helix type structures for higher power output deviceshas been dependent on thermal dissipation problems. Numerous examples ofprior art structures exist involving stubs, rods, straps or similarsupports combined with a helix to provide the prerequisite thermaldissipation. Such dissipative structures, however, have only resulted invery narrow bandwidth devices which renders them less attractive forhigh power microwave frequency electromagnetic energy devices. Inaddition to the thermal dissipation structures incorporated in highfrequency traveling wave devices, numerous methods of cooling have beenproposed incorporating direct or series cooling of the wave propagatingstructure or conduction cooling by means of a supporting heat sinkmember having internal means for circulating a cooling fluid.

It is desirable, therefore, to evolve a wave propagating structurecapable of broad bandwidths and high power outputs. High frequencyelectromagnetic wave energy generators and amplifiers must also becapable of traveling wave-electron interaction in the forward orbackward wave mode. The effciencies of M-type crossed field devicescoupled with broad frequency operating ranges will measurably improvemodern day electronic systems for communications, surveillance, weatherinformation and the like.

SUMMARY OF THE INVENTION In accordance with the teachings of theinvention, a crossed field traveling wave electron interaction devicewith a broad bandwidth and high power output capability is provided bymeans of a wave propagating structure having a modified helical circuitformat. Improved thermal dissipation is incorporated by aseries-parallel grouping arrangement for flow of the circulating coolingfluid with the individual wave circuit elements being continuouslyelectrically connected by an advancing member. The circuit elements areprincipally cooled by parallel flow to drastically improve coolingefficiency. In addition to the wide bandwidth capability, the wavepropagating structure is provided with programmed means for attenuatingthe propagated electromagnetic wave energy, as well as dissipatinggenerated'energy, by altering the dielectric constant of the coolingfluid at selected portions along the length of the propagatingstructure.

Another characteristic of the electron interaction device of theinvention is the efficient suppression of undesired space harmonics suchas those of the backward wave type when a forward wave device isdesired. The conductive interconnecting element for advancing thecircuit waves contacts adjacent periodic elements and provides forelectrical parameter considerations independently of the thermaldissipation problems. The embodiments may be of a linear or circularconfiguration and the periodic circuit elements may be solid or hollow,as

well as of a rectangular, square, triangular or circular cross sectionto adapt the device to the thermal and electrical characteristics fordesired bandwidth and power output. There is thus provided a unique andnovel device incorporating the high efiiciencies and high power outputsof an M-type interaction device with the broad bandwidths of an O-typein a unitary embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the detailsfor the provision of a preferred embodiment, will be readily understoodafter consideration of the following detailed description and referenceto the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of an illustrative embodiment of theinvention;

FIG. 2 is a perspective view of the wave propagating structure of theillustrative embodiment in a circular configuration;

FIG. 3 is an isometric view of a fragmentary portion of a wavepropagating structure of a directly cooled embodiment of the inventionin a linear array;

FIG. 4 is a cross-sectional view of a circular structure having a directcooling fluid circuit;

FIG. 5 is an isometric view of a directly cooled embodiment with eachperiodic circuit element having a separate insulator pp t;

FIG. 6 is an isometric view of an alternative embodiment of the wavepropagating structure circuit elements;

FIG. 7 is an isometric view of an alternative embodiment o the structureshown in FIG. 5 with the separate insulator support as well as amodified periodic circuit element;

FIG. 8 is a diagrammatic illustration of a series-parallel coolingcircuit for an illustrative embodiment of the invention;

FIG. 9 is an isometric view of a series-parallel periodic circuitembodiment of the invention;

FIG. 10 is amfi diagram of a wave propagating structure displaying stopband space harmonic suppression in accordance with the invention; and

FIG. 1 l is a graph of the reflection coefiicient versus frequency overthe operating range with the wave propagating structure incorporatingbackward wave suppression.

DESCRIPTION OF THE PREFERRED EMBODIMENT The crossed field electroninteraction device embodiment 2 incorporates a wave propagatingstructure 4 having broad bandwidth capability and improved thermaldissipation characteristics within an evacuated envelope 6. A soleelectrode 8 is disposed concentrically with respect to the wavepropagating structure 4 and is normally biased at a negative potential.An input electrical lead assembly 10 provides for the introduction ofelectron beam generation and electric field producing means. Magnetmembers 12 provide for the magnetic field distributed perpendicular tothe resultant electric fields.

The wave propagating structure 4 includes a plurality of substantiallyU-shaped parallel periodic circuit elements 14 supported by base member18 having fluid channels 20 and 22 with the elements interconnected byadvancing member 16. The base member 18 together with oppositelydisposed end plates 24 and 26 hermetically sealed thereto fonn theevacuated envelope 6 of the overall embodiment.

The sole electrode 8 comprises a cylindrical member of an electricallyconductive material having a web portion 28 defining a channel 30 forconfining an electron beam within an interaction space bounded by thechannel wall surfaces and the space wave propagating structure 4. Asource of electrons is disposed in a recessed portion within the soleelectrode 8 with the electrical connections provided through theassembly 10. For the sake of clarity the specific details of theelectron source have been omitted, however, the connections will'be madeto such conventional items as the cathode, heater, grid and acceleratingelectrodes by means of lead wires 34, 36, 38 and 40 extending throughglass bead 42 which is, in turn, supported by sleeve members 44 and 46having an intermediate glass member 48. The entire electrical leadassembly 10 extends within the hollow supporting member 50 which isinserted within a tubular member 52 in the web portion 28 of soleelectrode 8.

The electric field extending between the wave propagating structure 4'and sole electrode 8 is supplied by means of a unidirectional voltagesupply such as, for example, a source 54. The sole electrode 8 is biasednegatively by means of source 56 connected betweenthe lead 36 extendingto the cathode of the electron source and the electrode supportingmembers 44 and 50. The wave propagating structure 4 is maintained at apositive potential by voltage source 54 connected between sleeve 46 andthe base member 18 of the wave propagating structure.

Output coupling means of the well-known coaxial transmission type, aswell as a collector electrode, which may be fluid cooled, are disposedadjacent the output ends of the wave propagating structure and thepositions of these members will be described in connection with FIG. 2.Specific details have been omitted since these elements are ofwell-known construction in the interest of specifically describing thewave propagating structure of the present invention.

Reference is now directed to FIG. 3 disclosing a fragmentary portion ofan exemplary embodiment of a wave propagating structure 60 having asubstantially linear configuration. A plurality of periodic circuitelements 62 are uniformly disposed in parallel by means of bar type basemembers 64 and 66 of a nonconductive insulating material. The elementscomprise substantially U-shaped loop members and fabricated in eitherajsolid or tubular configuration in accordance with the cooling circuitpreferred. The base members 64 and 66 are fabricated fromany of thewell-known ceramic or dielectric materials employed in traveling waveelectron interaction devices to provide a minimum of dielectric loadingto interfere with the coupling impedance characteristics of thepropagating structure relative to the adjacent electron beam. It will benoted that the circuit elements 62 are thereby disposed in a parallelarray to measurably enhance higher power capabilities by reason of theincreased thermal dissipation efficiency. The base members 64 and 66 maybe mounted on a suitable heat sink member to provide the dissipation ofthe thermal energy by conduction or direct cooling. Alternatively. thebase member may comprise a single unitary slab of the applicablematerial supporting both ends of the circuit loop members or individualsleeve members.

Means for providing electrical continuity and advancing theelectromagnetic traveling wave energy propagated along the circuit areprovided by a plurality of electrically conductive elements 68interconnecting adjacent circuit elements 62 to thereby provide amodified helical delay line structure having the electrical propertiesfor deriving broad frequency range outputs of ()-type electroninteraction devices. Advancing elements 68 provide for the electricalcontinuity independent of thermal dissipation considerations which areprovided principally by the parallel cooling circuit. In a workingembodiment each of such elements comprise a solid planar surface memberhaving a substantially rectangular configuration of a highlyelectrically conductive metal, such as copper. The advancing members 68thereby provide a flattened asymmetrical surface to suppress undesiredspace harmonics, as will be hereinafter described, while the U-shapedmembers have been illustrated in a circular configuration to facilitatecooling fluid circulation. Many other configurations will be possible ineither the overall wave propagating structure or portions thereof tocustomize both the thermal and electrical properties. Such alternativeembodiments will also be discussed in relation to subsequent views. 7

Referring next to FIG. 4 a cooling circuit for the wave propagatingstructure 60 disclosed in FIG. 3 is illustrated. In this embodiment theperiodic circuit loop elements 70 are of a tubular configurationdefining a hollow passageway 72. The interconnecting solid advancingelements are similar to that shown and described in relation to FIG. 3and have been similarly numbered 68. The insulator base members 74 and76 are provided with a plurality of aligned rows of apertures 78 and 80to facilitate the circulation of the cooling fluid through each circuitloop element 70 without shorting out these circuit elements to themetalic back wall member 82 which also provides a plurality of alignedapertures 84 and 86. Back wall member 82 abuts a circulating coolingfluid jacket member 88 defining hollow passageways 90 and 92 togetherwith inlet and outlet conduits 94 and 96. The jacket member 88 may befabricated of a metallic structure to facilitate removal of thermalenergy. Partition member 98 separates passageways 90 and 92 to therebyprovide for the parallel cooling of the circuit loop elements 70. In theillustrated embodiment the wave propagating structure has been disclosedin the circular configuration and is readily adapted to the crossedfield device shown in FIG. 1. The cooling fluid circuit may be arrangedin any manner desired as will be hereinafter evident by groupingindividual circuit loop elements to handle an increased flow of thecooling fluid in predetermined portions of the wave propagatingstructure where intense thermal energy is generated by interaction withthe adjacent traversing electron beam.

Referring next to FIGS. 2 and 5 an alternative embodiment of theinvention is disclosed which may be fabricated in either the linear orcircular configuration. The periodic circuit loop elements 100 whichagain may be of either a solid or hollow configuration, as well ascircular or flat or a combination thereof, are supported at their endsby individual insulator base members such as sleeves 102 and 104. Thesleeves isolate the traveling wave propagating structure from themetallic envelope body member 106 incorporating the cooling circuitpassageways 108 and 110. An upper and a lower partition member 1 l2 and1 14 provide for the disposition of a separate cooling circuit to handlethe group of parallel periodic circuit loop elements encompassed by thebracket 101. The interconnecting advancing electrically conductivemembers 116 are again shown as of a solid rectangular cross section. Inthe embodiment shown in FIG. 2 a short length of metallic conduit 1 18has been shown to mate with the ends of the sleeve members 102 and 104to facilitate the fabrication of the overall wave propagating structure.

In FIG. 2 the passageway 120 in the envelope body member 106 isindicated to receive the structure for coupling input electromagneticwave energy from an external source for a crossed field amplifierdevice. The amplified energy after traversing the wave propagatingstructure is coupled to a utilization circuit through output coupler122. In the illustrative device the electron source is disposed withinthe sole electrode recess previously described in the region of theinput end of the structure. In accordance with well-known teachings inthe art a collector electrode will be disposed within the body memberrecess 124 adjacent to the output end to complete the circuit for theinterception of the electron beam after interaction with the wavestraveling along the propagating structure. The collector may also befluid cooled in accordance with well-known practices. It will be notedthat in this embodiment approximately two-thirds of the overall wavepropagating structure will be cooled by a common source communicatingwith passageways 108a and 110a terminating in partition members 114 and1 16. The more efficient cooling circuit, therefore, will be disposedadjacent the remaining one-third of the overall wave propagatingstructure adjacent to the collector and energy output end. Since theelectron beam-wave interaction is at its maximum level over thisapproximate one-third length of the propagating structure, maximumcooling efficiency for the dissipation of the generated thermal energywill be provided with the structure of the invention. In this manner anyother desired programmed and customized cooling circuit may be providedtailored to the intended use taking into consideration both electrical,as well as thermal considerations.

The embodiments of the invention shown in FIGS. 1-5 inclusive allprovide for the uniform disposition of the periodic circuit loopelements, as well as the disposition of the insulating sleeve members102 and 104 which will suffice for most of the intermediate frequencyranges in the microwave spectrum of the electromagnetic energy band. InFIG. 6 an illustration of the staggered insulating support technique isshown which is extremely useful in extending the usage of the helixdelay line wave propagating structure to other frequency bands withinthe spectrum. The wave advancing element 126 also has been shown inanother alternative configuration with the point of interconnection tothe circuit loop elements 128 being disposed intermediate to the bends129 and 130 and the staggered array of insulator sleeve support members132 and 134 of a ceramic composition. In this embodiment, which may bedirectly cooled short, conduit sections 136 and 138 of alternatelyvarying length are affixed to the insulator members 132 and 134 forconnection to suitable cooling fluid circulating means. Since in devicesof the type under consideration the pitch or tum-to-tum capacitance iscontrolled by conventional electrical design considerations, a point isreached, particularly at the high microwave frequencies where theinsulating sleeve members supporting the individual circuit loopelements have a wall thickness which is mechanically impractical. Thestaggering of the insulating support members 132 and 134 permits theutilization of much thicker insulating sleeve support members withoutdegrading the electrical properties of the helical delay line structure.In this manner either a low voltage device with its attendant smallpitch value or a very high microwave frequency device having exceedinglysmall wavelengths may be realized. Even at lower or intermediatefrequencies the use of this staggered support technique will permit theutilization of much thicker insulating sleeve support walls for directlycooled tubular configurations and thus provide a much stronger assembly.The removal of the wave advancing element 126 from a position adjacentto the insulating sleeve support members will also reduce to a minimumthe dielectric loading of the wave propagating structure to furtherenhance the electron coupling electrical characteristics.

In FIG. 7 still further alternative embodiments are shown. A pluralityof periodic circuit loop elements 140 are supported by a unifonnlydisposed array of insulating sleeve support members 142 and 144 similarto that shown in FIG. 5. Each of the circuit loop elements 140 may beprovided with a circular cross section along the portions 145 and 146adjacent to the insulating sleeve support members and this element mayalso be provided in the hollow or solid configurations. The intermediateportion of the circuit loop members disposed coplanar to the surface ofthe sole electrode 8 or parallel to the disposition of the magneticfields adjacent to the traversing electron beam are provided with aplanar surface 148 which may be either square or rectangular. The planarconfiguration will provide a cross-sectional area which materiallyaffects the electrical characteristics of the propagating waves bymaintaining a uniformly controlled spacing between the respectiveelements. Further, a flat helix loop surface will facilitate the thermaldissipation by increasing the heat transfer interface while a circularcross-sectional area has a tendency to reduce such a heat transfer area.In numerous instances a compromise between the respective desiredthermal and electrical parameters may result in a combined structuresuch as that illustrated in FIG. 7 with the circular and flat sectionsor in certain instances it may be advantageous to employ complete flatcircuit element configuration commencing from the insulator support. Inthe disclosed embodiment for direct cooling, it will be advantageous toprovide a circular passageway through the circuit loop element toenhance the flow rate of the cooling fluid circulating through thecircuit. The tum-to-tum capacitance for the planar configurations willbe at a maximum for a rectangular cross section and a minimum for atriangular cross section. It is also within the purview of the inventionto incorporate various surface configurations exposed to the electronbeam in varying regions of the overall interaction region taking intoconsideration both thermal and electrical considerations.

Referring now to FIGS. 8 and 9 other unique features of the presentinvention will be described. The individual circuit elements combiningto form the overall propagating structure are disposed in a parallelarray. The circulating cooling fluid, therefore, will be circulatedthrough the individual turns to thereby provide the maximum thermaldissipation efficiency. A variety of cooling circuits may be employed inthe applicable devices to provide a maximum cooling in the region ofhighest thermal energy generation by grouping certain individual circuitloop elements into programmed groupings with one section of the overallstructure such as, for example, one-third and two-thirds with theseparallel groupings then being connected in series. In FIG. 8 the fluidcooling jacket member 150 of a metallic or other thermally conductivematerial has an inlet conduit 152 and outlet conduit 154. The pluralityof circuit loop elements forming the predetermined smaller or one-thirdsection of the overall wave propagating structure are indicatedgenerally by the numeral 156 defining a plurality of passageways 158within parallel grouping section 160. An example of the application ofthe invention would be the disposition of the one-third section havingthe lower temperature cooling fluid adjacent the output section of thedevice where much higher thermal energy results from electron beam-waveinteraction. The net effect will thereby be the provision of a coolingliquid flow within section 160 at substantially twice the flow rate ofthe remainder of the wave propagating structure. The parallel groupingsection 162 incorporates loop circuit elements 164 defining passageways166 in a parallel array. A partition member 168 between the sections 160and 162 will provide for the circulation of the cooling fluid from acommon source. In the previously discussed embodiment in FIG. 2, twosuch partition members 1 12 and 114 are provided in the upper and lowerpassageways which would require the use of two independent coolingsystems rather than a single closed loop. It may be advantageous in manyinstances to incorporate two such complete cooling circuits to provideeven higher output withoutunnecessarily high total flow of such fluids.

. In FIG. 9 an'embodiment of a series-parallel cooling fluid circuitillustrates the thermal dissipation characteristics with individualgroupings of the circuit loop elements. The wave propagating structure170 incorporates the plurality of parallel periodic circuit loopelements 172 with uniformly disposed insulating support members 174 and176 together with interconnecting wave advancing elements 178 removedfrom the face of the insulating support members collectively defining ahelical delay line structure. Circuit elements 172a are interconnectedby means of a conduit 180 to couple the system to the low temperatureend of the cooling circuit at the inlet con- .duit. The remaining or,illustratively, four loop elements designated by the numeral l72b areinterconnected by conduit 182 to couple the cooling circuit to the,output end. An

end ofthe respective loop element 172a and 17217 are, therefore,interconnected in a parallel manner by means of conduits 180 and 182while the opposing ends of all of the circuit loop elements collectivelydefining the overall wave propagating structure are interconnected by acommon conduit 'member 184. This series-parallel cooling circuitarrangement will, therefore, concentrate the highest thermal energydissipation means utilizing the most efficient coolant temperatures.

. .Another. feature of the invention resides in the selection ofthecooling fluids for use in the variety of cooling circuits andpropagating structure configurations. As is known in the art, thecooling fluidhas a material effect on the electrical characteristics ofthe wave propagating structure. The insulating support members of adielectric or ceramic material together with the circulating fluidcomprise a shunt resistance to ground in addition to the dielectricloading. Dependent on the loss tangent characteristic of the coolingfluid, the shunt resistance characteristic varies, as well as theattenuation, along the wave propagating structure. The shunt resistanceis also materially affected by the length of the fluid path. If themechanical and thermal dissipation considerations would permit, thecirculating conduits could be made rather lengthy in order that acooling fluid such as water with its excellent cooling properties butpoor loss temperature would not affect attenuation. The dielectricproperties of the cooling fluid also affect the frequency determiningproperties of the wave propagating structure. An increase in thedielectric constant is equivalent Comings DC-200 or Minnesota Mining andManufacturing Companys FC- may be employed without adversely affectingthe electrical properties. The additional advantage incorporated in thepresent invention is the means for introducing attenuation losses wheredesired alongspecific predetermined portions of the wave propagatingstructure simply by using a lossy coolant such as water in certainsections of the wave propagating structure. Attenuation can also beachieved in an alternative manner by coating the insulating supportmembers with a lossy material which will rapidly absorb any thermalenergy. Since the cooling fluid traverses through the insulatingmembers, the exceedingly high thermal energy absorbed therein will berapidly removed.

A remaining feature of the invention to be discussed comprises a meansfor introducing an asymmetry in thepropagation of the electromagneticwaves to thereby suppress undesired space harmonics such as the backwardwave-determining component which may be coupled to the wave 7propagating along the helical structure. To avoid theinteracconfiguration of the wave advancing members 16, 68, 116,.

126, and 178 in the previous illustrations, it will be noted that a flatelectrically conductive member is provided. This configuration incombination with the remainder of the wave propagating structureintroduces the asymmetry which results in a stop band at a frequencywhere the backward wave space harmonic generation adversely affects theoperation of the device. In FIG. 10 the curve plotting themficharacteristics of the wave propagating structure of the invention isshown with the stop band indicated in the region 186. This stop'banddesign will facilitate the operation of the wave propagating structureat a much higher value for ka which is normally at 0.25. In FIG. 11 aplot of the reflection coefficient over the frequency band of operationis shown for a working embodiment of a helical circuit structure havingthe inherent backward wave suppression feature. The operating range isdesignated by the curve'l88 and the stop bandby the space There is thusdisclosed a unique traveling wave electron interaction device having apropagating structure with broad bandwidth characteristics.Additionally, an external adjacent electron beam in an interactionregion commonly employed in crossed field devices with its high powergeneration capability provides for a very high efficiency deviceincorporating the inherent advantages of both M- and O-type structures.Thermal and electrical considerations are considered substantiallyindependent of one another with a principally parallel thermaldissipation circuit with its measurably increased cooling efficiencycombined with an electrically continuous wave propagating structure foradvancing the electromagnetic wave energy to yield power outpumheretofore unattainable in electron discharge devices of the prior art.The periodic wave propagating structure provides a means for the moreefficient thermal dissipation overregions of electron interactionyielding the highest thermal problems. Suppression of undesired spaceharmonics, as well as 'means for providing attenuation through selectiveutilization of cooling fluids, provide still further advantages in aunitary device. Some modifications and alterations in the pertinentstructures have been heretofore described in detail and numerous othermodifications will be readily apparent to those skilled in the art. Itis intended, therefore, that the foregoing illustrative embodiments anddetailed description be considered in its broadest aspects and not in alimiting sense.

What is claimed is:

1. In combination:

means for directing a beam of electrons along a predeterminedinteraction path; means for propagating electromagnetic wave energyadjacent to said path in energy exchanging relationship with said beam;7

said propagating means comprising predetermined groupings of a pluralityof hollow periodic parallel disposed circuit elements with each of saidelements having at least one end supported by nonelectrically-conductivemeans;

an electrically conductive member interconnecting adjacent elements toadvance said wave energy; and

means for circulating a cooling fluid through said circuit elements;

said-groupings of circuit elements being serially interconnected toprovide programmed thermal dissipation over selected regions of saidpropagating means.

2. A periodic electromagnetic wave propagating structure comprising:

wherein said grouping of elements for more intense thermal energydissipation covers a minor portion of the overall structure length.

4. A crossed field electron interaction device comprising:

an envelope;

a periodic electromagnetic wave energy propagating structure; I 1

an electrode coextensive with and spaced from said structure to definean interaction path;

means for generating and directing a beam of electrons along said pathin energy exchanging relationship with said wave energy traveling alongsaid structure;

crossed electric and magnetic fields disposed with said interactionpath;

said wave propagating structure comprising predetermined groupings of aplurality of hollow periodic parallel disposed circuit elements eachsupported by nonelectrically conductive means; and

an electrically conductive member for providing electrical circuitcontinuity interconnecting adjacent elements; output means for couplingenergy appended to one end of said propagating structure; and

means for circulating a cooling fluid through said circuit elements;

said groupings of circuit elements being serially interconnected toprovide for programmed more intense thermal energy dissipation overselected regions of said propagating structure.

5. The device according to claim 4 wherein one region provides for moreintense thermal energy dissipation over approximately one-third of theoverall length of said propagating structure adjacent to the outputenergy coupling end.

6. The device according to claim 4 wherein said region of more intensethermal energy dissipation is coupled to separate means for circulatinga cooling fluid independently of the remainder of the wave propagatingstructure.

1. In combination: means for directing a beam of electrons along apredetermined interaction path; means for propagating electromagneticwave energy adjacent to said path in energy exchanging relationship withsaid beam; said propagating means comprising predetermined groupings ofa plurality of hollow periodic parallel disposed circuit elements witheach of said elements having at least one end supported bynonelectrically-conductive means; an electrically conductive memberinterconnecting adjacent elements to advance said wave energy; and meansfor circulating a cooling fluid through said circuit elements; saidgroupings of circuit elements being serially interconnected to provideprogrammed thermal dissipation over selected regions of said propagatingmeans.
 2. A periodic electromagnetic wave propagating structurecomprising: a plurality of parallel disposed hollow circuit elements ina cooling array with predetermined programmed groupings of said elementsfor intense thermal energy dissipation over a selected portion of theoverall length of the structure; said elements being supported bynonelectrically-conductive means; said groupings of circuit elementsbeing serially interconnected; an electrically conductive memberinterconnecting adjacent elements to advance said wave energy; and meansfor circulating a cooling fluid through said circuit elements.
 3. Thewave propagating structure according to claim 2 wherein said grouping ofelements for more intense thermal energy dissipation covers a minorportion of the overall structure length.
 4. A crossed field electroninteraction Device comprising: an envelope; a periodic electromagneticwave energy propagating structure; an electrode coextensive with andspaced from said structure to define an interaction path; means forgenerating and directing a beam of electrons along said path in energyexchanging relationship with said wave energy traveling along saidstructure; crossed electric and magnetic fields disposed with saidinteraction path; said wave propagating structure comprisingpredetermined groupings of a plurality of hollow periodic paralleldisposed circuit elements each supported by nonelectrically conductivemeans; and an electrically conductive member for providing electricalcircuit continuity interconnecting adjacent elements; output means forcoupling energy appended to one end of said propagating structure; andmeans for circulating a cooling fluid through said circuit elements;said groupings of circuit elements being serially interconnected toprovide for programmed more intense thermal energy dissipation overselected regions of said propagating structure.
 5. The device accordingto claim 4 wherein one region provides for more intense thermal energydissipation over approximately one-third of the overall length of saidpropagating structure adjacent to the output energy coupling end.
 6. Thedevice according to claim 4 wherein said region of more intense thermalenergy dissipation is coupled to separate means for circulating acooling fluid independently of the remainder of the wave propagatingstructure.